Influence of heat treatment and cutting speed on chip segmentation of age hardenable aluminium alloy

Abstract

A change in chip shape has been observed as a function of age hardening and cutting speed during high speed milling of the aluminium alloy 7075. In order to study this effect systematically, the aluminium alloy was heat treated to produce different precipitation states and machined under carefully controlled conditions at cutting speeds between 1000 and 7000 m min^-1. The underaged state shows local shearing producing segmented chips. The degree of segmentation increases with cutting speed. In contrast, the overaged state shows continuous chips up to the highest cutting speeds. The chips obtained with the peak aged state show a fluctuation between segmented and continuous parts. These results can be understood in terms of the differing work softening/hardening behaviour of the under- and overaged states owing to the specific interactions between dislocations and precipitates during chip formation.     

Effects of rheocasting and heat treatment on microstructure and mechanical properties of A356 alloy

The effects of the rheocasting process and T5 heat treatment on microstructure and mechanical properties of A356 alloy were investigated. The results show that the temperature range for the solid-liquid state is roughly between 560 °C and 630 °C, and the solid fraction increases from 0% to 100% with decreasing temperature. The finer microstructure in rheocasting in comparison with the one in conventional casting was attributed to pressure breaking down the secondary dendrite arms, especially for specimens around 600-610 °C. It was proved that rheocasting specimens have improved mechanical properties over the conventional casting ones. Furthermore, the result shows that T5 heat treatment can strengthen A356 alloy, while the plasticity was reduced at the same time.     

High Strength AA7050 Al alloy processed by ECAP: Microstructure and mechanical properties

Commercial AA7050 aluminium alloy in the solution heat-treated condition was processed by ECAP through routes A and B_C. Samples were processed in both room temperature and 150 °C, with 1, 3, and 6 passes. The resulting microstructure was evaluated by optical microscopy (OM) and transmission electron microscopy (TEM). Only one pass was possible at room temperature due to the low ductility of the alloy under this condition. In all cases, the microstructure was refined by the formation of deformation bands, with dislocation cells and subgrains inside these bands. The increase of the ECAP temperature led to the formation of more defined subgrain boundaries and intense precipitation of spherical-like particles, identified as η′ and η phases. After the first pass, an increase in the hardness was observed, when compared with the initial condition. After 3 passes the hardness reached a maximum value, higher than the values typically observed for this alloy in the overaged condition. The samples processed by route B_C evolved to a more refined microstructure. ECAP also resulted in significant strength improvement, compared to the alloy in the commercial overaged condition.     

Residual stress relief in the aluminium alloy 7075

The residual stresses in heat-treated 7075 aluminium alloy blocks have been characterised using two neutron diffraction strain scanning instruments. The influence of uniaxial cold compression on relieving the residual stress has been determined. Systematically increasing the magnitude of cold compression from 1 to 10% has been shown to have a small beneficial effect on the final residual stress distribution, by reducing the magnitude of the range in the triaxial residual stresses. The effect of an overaging precipitation treatment on the residual stress has also been characterised, and this was found to have a significant stress relieving influence (25–40%). A relationship between the width of the {311} diffraction peaks and the amount of cold compression was also observed.     

Effect of heat treatment on small scale fragmentation of aluminium alloy

Abstract

Small scale explosions, using a detonator, of 7075 aluminium alloy cylinders, 15–100 mm outside diameter, were carried out to investigate the effects of heat treatment on fragmentation. This was the finest for the strongest as received alloy and coarsest for the softest overaged alloy. This effect was similar to that seen in investigations of the fragmentation of steel. Cylinders of 50 and 100 mm in diameter did not fragment but plastically deformed with maximum deformation at the cylinder bottom. Fragmentation of 33 and 42 mm diameter cylinders produced long fragments typical of the break-up of thick walled cylinders. At smaller diameters, break-up gave fragments of several shapes, finer fragments being largely associated with the smallest diameter cylinders and the highest strength alloys. Results followed those seen in large scale studies of cylinder break-up and suggest the possibility of using small scale fragmentation experiments in the investigation of the effects of composition, heat treatment and processing on natural fragmentation.     

电磁铸造5182铝合金锭的组织与性能研究

采用电磁铸造技术铸造了易拉罐用5182变形铝合金，采用光学显微镜和扫描电镜分析了其显微组织，而且对其进行了均匀化处理和对比实验。结果表明，电磁铸造锭有更加良好的内部组织和优良的力学性能，电磁铸造试样的硬度大约是普通连续铸造试样的两倍，疲劳性能是普通连续铸造铸锭的3倍，电磁铸造铸锭还有良好的耐磨性，电磁铸造锭的优良性能得宜于电磁搅拌的作用使整个铸锭获得均匀细小的晶粒组织，电磁铸造技术是一种无模铸造技术，它依靠电磁力约束液体金属成型，液体金属不与铸模接触，铸锭表面光滑如镜；相反，普通连续铸造锭表面因存在振动痕和亚表面偏析等铸造缺陷，力学性能大大降低。     

Effects of ultrasonic treatment on microstructure and mechanical properties of 6016 aluminium alloy

Ultrasonic treatment was applied during solidification forming of 6016 aluminium alloys. The effects of ultrasonic vibration on the microstructure and mechanical properties of the 6016 aluminium alloy ingot were studied. Compared with conventional casting, the ingot prepared with ultrasound applied to the molten metal had a fully refined microstructure and greater material homogeneity. Ultrasonic treatment reduced the amount of porosity developed by embedded gas and also resulted in an obvious decrease in solidification defects, like shrinkage. In addition, component segregation was minimised and the mechanical properties were enhanced.     

Uphill quenching to reduce residual stress in a heat treatable aluminium alloy

Three rectilinear blocks of the aluminium alloy 7449 were characterised using neutron and X-ray diffraction. One block was heat treated normally and two blocks were subject to uphill quenching from ?196°C to 100°C. Boiling water and steam were used to rapidly increase the temperature of the blocks to reverse the thermal gradients introduced by cold water quenching. It was possible to detect the beneficial influence of uphill quenching on residual stress using either fluid. The influence of steam was very effective but localised and limited to the surface in close proximity to the steam jet. For more uniform stress relief, multiple steam jets will be required to ensure the entire surface receives a significant thermal input.     

Effects of heat treatments on the microstructure and mechanical properties of a 6061 aluminium alloy

This paper describes the mechanical behavior of the 6061-T6 aluminium alloy at room temperature for various previous thermal histories representative of an electron beam welding. A fast-heating device has been designed to control and apply thermal loadings on tensile specimens. Tensile tests show that the yield stress at ambient temperature decreases if the maximum temperature reached increases or if the heating rate decreases. This variation of the mechanical properties is the result of microstructural changes which have been observed by Transmission Electron Microscopy (TEM).     

TI-6Al-4V合金置氢-除氢组织与力学性能

为研究除氢处理对置氢钛合金组织与性能的影响,对Ti-6Al-4V合金在不同参数条件下进行了置氢与除氢处理,采用光学显微镜分析了置氢-除氢处理过程中Ti-6Al-4V合金微观组织的演化规律,通过室温拉伸试验研究了置氢-除氢处理后Ti-6Al-4V合金的力学性能,探讨了Ti-6Al-4V合金置氢-除氢组织与力学性能之间的相...     

Influence of low magnitude plastic strains on residual stress in 7075 aluminium alloy

The effect of post quench delay on residual stress has been determined by subjecting four rectilinear blocks of quenched 7075, containing large residual stress magnitudes, to small (<1.0%) plastic strains applied by cold compression. One experiment kept the plastic strain the same in all samples (～0.12%) by cold compressing simultaneously in one pressing. The second pressed the blocks separately to the same strain (～0.45%). The post quench delays were <10, 60, 120 and 240 min. The residual stresses were characterised using neutron and X-ray diffraction. It was possible to detect the impact of the small plastic strains on all samples, but the diffraction measurement techniques could not conclusively isolate the influence of the post quench delay.     

Microstructure and mechanical properties of high power diode laser (HPDL) treated cast aluminium alloys

The appliance and development of modern technologies in the areas of surface engineering can be extended by laser surface treatment, especially using high power diode laser (HPDL) for remelting, feeding and/or alloying. The purpose of this work was to determine technological and technical conditions for tungsten carbide (WC) ceramic powder feeding into the surface layer of the laser treated Al–Si–Cu cast aluminium alloys with high power diode laser, as well as to investigate the microstructure and ceramic powder particle distribution in the surface layer. Special attention was devoted to monitoring of the layer morphology of the investigated material and on the particle occurred. Light and scanning electron microscopy as well as X‐Ray diffraction were used to characterize the microstructure of the remelted zone. A wide range of laser powers was choose and implicated by different process speed rates. Also one powder in form of tungsten carbide was used for feeding with the middle particle size of 80 µm. As the main findings there was found that, the obtained surface layer is without cracks and defects as well as has a comparably higher hardness value compared to the non remelted material. The hardness value increases according to the laser power used so that the highest power applied gives the highest hardness value in the remelted layer. Also the distribution of the tungsten carbide particles is good, but there are still possibilities for further modelling. The major purpose of this work is to study the effect of a high power diode laser melting on the cast Al–Si–Cu alloys structure to provide application possibilities for automotive and aviation industry.     

Microstructure, local and global mechanical properties of friction stir welds in aluminium alloy 6005A-T6

The effect of the welding speed on the microstructure, local and overall mechanical properties of friction stir welded joints has been investigated in the aluminium alloy 6005A-T6. The fine hardening precipitation within the heat-affected zone has been characterized by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Post-welding heat treatments have been applied to obtain indications on the level of solid solution supersaturation in the as welded state. The local mechanical behaviour was determined using thin specimens extracted from various regions of the weld. The overall properties were measured on samples cut perpendicular to the weld. Specific attention was devoted to the relationship between the local microstructure and local hardening properties in the weakest region, which govern the overall strength and ductility of the welds.     

Microstructure and properties of laser clad high-entropy alloy coating on aluminium

An AlCrFeNiCuCo high-entropy alloy (HEA) coating was synthesised on an aluminium substrate by laser cladding. Samples were characterised using an optical microscope, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, a microhardness tester, and an electrochemical workstation. The results showed that the interface between the cladding layer and matrix was sound, while the HEA coating consisted of BCC and FCC solid solutions and an Al-rich phase resulting from substrate dilution. The microstructure of the clad layer comprised both columnar and equiaxed grains. The average microhardness of the coating was 550 HV_0.2, and it exhibited better corrosion resistance than the aluminium matrix in a 1?mol?L^?1 H₂SO₄ solution. The typical corrosion characteristic of the coating was pitting and localised corrosion.     

Microstructure and properties of A357 aluminium alloy treated by pulsed magnetic field

This study examined the effects of a pulsed magnetic field (PMF) on the solidified microstructure and properties of A357 aluminium alloy. Results showed that the solidified microstructure of the alloy treated by a PMF was refined. The treated alloy in the T6 state had superior mechanical properties, with the ultimate tensile strength, yield strength and elongation increasing by 48?MPa (18.5%), 46?MPa (16.4%) and 4.8% (142%), respectively, when compared with the untreated alloy. When testing at room temperature, with a strain amplitude of 1?×?10^?4 and at a frequency of 1?Hz, the damping capacity value was 14.2?×?10^?3 for the alloy subjected to a PMF treatment, which increased by nearly 170% when compared with the untreated alloy.     

Al_xCoCrFeNiCu_2高熵合金的组织结构及力学性能

采用真空电弧熔炼技术制备出不同Al含量的AlxCo Cr Fe Ni Cu2的高熵合金,研究Al含量对该高熵合金的微观组织及力学性能的影响。结果表明,该铸态高熵合金合金具有简单的bcc相固溶体结构及fcc相固溶体结构。AlxCo Cr Fe Ni Cu2(x=1,2和3)合金中fcc相固溶体的含量在增加;当x=4,5时,合金中bcc相固溶体的含量增加。合金的硬度随着Al元素的增加而提高。制备出的5种合金中Al4Co Cr Fe Ni Cu2硬度值最高。Al3Co Cr Fe Ni Cu2高熵合金具有较高的屈服强度和断裂强度。     

Characterisation and modelling of toughness in 6013-T6 aerospace aluminium alloy friction stir welds

The effect of the friction stir welding process on the toughness properties of AA6013-T6 sheet has been investigated. The alloy was received and welded in the peak aged T6 condition and the toughness measured at intervals across the weld by means of a notched tear test, with subsequent fractographic examination via field emission gun scanning electron microscope (FEGSEM) and microstructural characterisation via optical microscopy and energy dispersive X-ray (EDX). It is shown that the controlling factors for toughness in AA6013-T6 following FSW are the population and distribution of the coarse α-(Al,Fe,Si,Mn) intermetallic particles, with strength variations caused by precipitate dissolution, coarsening and transformation representing a secondary consideration. Minimum toughness occurs at the boundary between the weld nugget and the heat-affected zone due to the alignment and concentration of coarse particles at this point by the FSW process. A simple model is implemented and provides a reasonable prediction of the weld toughness from simple microstructural observations.     

The effect of pre-straining on the mechanical behaviour of self-piercing riveted aluminium alloy sheets

Self-piercing riveting as an alternative joining method to spot-welding has attracted considerable interest from the automotive industry and has been widely used in aluminium intensive vehicles. Pressing and stamping are important processes in automotive production and result in additional straining on the vehicle body sheet material. It is therefore important to have knowledge of the effect of sheet pre-straining on the quality of the self-piercing riveted joints and on the mechanical behaviour of the riveted aluminium alloy sheets. This paper reports the influence of sheet pre-straining on the static and fatigue behaviour of self-piercing riveted aluminium alloy sheet. Wrought aluminium alloy sheet, NG5754 with a nominal thickness value of 2 mm was used to obtain pre-strained NG5754 sheets with pre-straining levels of 3%, 5% and 10%. Pairs of pre-strained NG5754 sheets were joined to create single-riveted lap joints which subsequently underwent lap-shear and fatigue testing. Microscopic inspection showed that the joint quality was satisfactory despite the increasing sheet straining levels. The results showed that by increasing the pre-straining level up to 10%, the shear and fatigue strength also increased. The rate of increase of the static and fatigue strength differed as the pre-straining levels varied.     

一种新的铝合金晶界检测算法及应用

晶粒度检测是金相检验中的一个重要问题，在应用图像处理方法时体现为边缘检测，原有的边缘检测算法的各向同性的特点导致边缘提取的效果不理想，本文通过对图像边缘的分析，提出一种新的边缘检测算法，设计出一种各向异性，权重合理的边缘检测算子。与传统的边缘检测算法实验结果的比较显示了其优良的性能，在铝合金的晶界检测中取得了较好的效果。